We propose to apply digoxin and dihydrodigoxin radioimmunoassay methods to the study of clinical factors which may affect the absorption and metabolism of the cardiac glycoside, digoxin. We propose to study the effects of Fab fragments of antidigoxin antibodies on the metabolic fate of digoxin in patients receiving these Fab fragments for the reversal of severe digoxin intoxication; we also plan to study the metabolism of the Fab fragments themselves in patients so treated. We propose to employ antibodies to a digitalis receptor, Na+, K+-ATPase, in studies of the function, localization, and tissue concentration of the ATPase complex. We propose to employ a newly developed radioimmunoassay for the B-adrenergic blocking drug, propranolol, in studies of patients receiving this drug for the treatment of hypertension, angina pectoris and certain arrhythmias. We propose to continue to elicit antibodies which react with specific segments of the fibrinogen molecule and its enzymatically derived products, with the goal of developing additional radioimmunoassay methods for the study of the coagulation process in vitro and for the study of clinical disease states characterized by intravascular thrombosis. BIBLIOGRAPHIC REFERENCES: Nossel, H.L., Butler V.P., Jr., Wilner, G.D., Canfield, R.E., and Harfenist, E.J.: Specificity of Antisera to Human Fibrinopeptide A Used in Clinical Fibrinopeptide A Assays. Thrombos. Haemostas. 35:101-109, 1976. Smith, T.W., Haber, E., Yeatman, L., and Butler, V.P., Jr.: Reversal of Advanced Digoxin Intoxication with Fab Fragments of Digoxin-Specific Antibodies. New Engl. J. Med. 294: 797-800, 1976.